The measured resonance signal exhibits large broadening and a rather complicated line shape. The observed signal broadening, on the order of 10 GHz, is many orders of magnitude larger than the intrinsic linewidth of the Rydberg transition [1]}. As shown in the following section, this large broadening arises due to the inhomogeneous broadening of the Rydberg transition of SE in the central channel because of the variation of the pressing electric field \(E_\perp \)  across the channel. It is harder to account for the rather irregular asymmetric shape of the signal. In addition, it should be noted that the detection method realized here does not measure the transition rate directly, instead, it probes the electron conductivity in response to the transition-induced heating of SE. In order to fully account for the shape of such a conductivity response one has to consider dependence of the electron temperature on \(V_\textrm {ch}\) , the corresponding change in the conductivity and measured current, etc. Also note that the electron density \(n_s\)  in the central channel varies with \(V_\textrm {ch}\) . Accounting for all these effects is a rather formidable task at the moment and is beyond the scope of the present report.
